Antoine LeCoultre started in Le Sentier after he invented a machine that cut watch pinions. In 1844 he built the Millionomètre, the first instrument to measure a thousandth of a millimeter, and in 1847 a winding system that did away with the watch key.
LeCoultre began working with the Paris watchmaker Edmond Jaeger in 1903, and the company took the name Jaeger-LeCoultre in 1937. It made the Calibre 101, still the smallest mechanical movement ever produced. The story goes that polo players in India asked for the Reverso. Richemont has owned the company since 2000.